Safety & Survival of Electric Cables

Safety & Survival of Electric Cables

Presented by

Lokman A. Dahlan

Technical Advisor

Design Requirements

• Satisfies power needs

• Flexible

• Reliable

• Has long life

• Minimal maintenance

• Economic

In relation to electric cables, safety..

• Is not a design requirement

• Prescribed by system designer

• Constructed as prescribed

• Appropriately installed by

trained/competent installer

• Safely managed by users

5

10 0 0 0 0 0 0 0 0 0 0

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3

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15

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25

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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

FA

ILU

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S

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Cable Life Cycle

Initiation

stage The golden yearsThe

EndRetirement age

Years <1

Phase Initiation stage

Failure freq Diminishing

Key suspectsinstallation

(workmanship)

Actionrepair & make

good

0-35

The Golden years

Erratic - low

physical damage (external)

cut & joint

30-40

The Pensioner

Erratic - high

imperfections (internal)

replace cable length

>40

The End

Increasing, exponentially

"unknown" (expired)

replace cable lengths

5

1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 02

0 13

58

18

28

0

10

20

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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

FA

ILU

RE

S

YEARS IN SERVICE

Cable Life Cycle

Cable life is..

The end of useful life

• Upon reaching a state of system instability

OR

• As prescribed by “experts” and/or from

experience

Cable life ?

Cable Life – Contributing Factors

• Internal – the requirements of specifications & relevant

standards, construction, manufacture, tests and transportation

of cables to site

• Operational – the manner of handling, installing, jointing &

terminating, loading and servicing as per system design

• External – the conditions endured by the cables in service

The quadrants of cable life

Designedas required,

installed & operated as intended

Installed & operated as intended,

NOT designed as required

Designedas required,

NOT installed or operated as intended

NOT designed,NOT installed or

operatedas intended

Cable Standards - International

• IEC 60227 Polyvinyl Chloride insulated cables 450/750V

• IEC 60502 Cables with extruded insulation 1-33kV

• IEC 60055 Paper Insulated 1-33kV• IEC 60840 Tests for cables with extruded

insulation >33 - 150kV• IEC 60811 Common test methods for

cable insulation and sheaths• IEC 60287 Calculation of Current Rating

Malaysian Standards (MS) on Cables

1 MS 2108: 2007 Electric Cable : 6.35/11(12)kV single core XLPE insulated cables – non-armoured

2 MS 2109: 2007 Electric Cable : 6.35/11(12)kV single core XLPE insulated cables – armoured

3 MS 2110 :2007 Electric Cable : 19/33(36)kV single core XLPE insulated cables – non-armoured

4 MS 2111: 2007 Electric Cable : 19/33(36)kV single core XLPE insulated cables –armoured

5 MS 2113* Electric Cable : 12.7/22(24)kV single core XLPE insulated cables – non-armoured

6 MS 2114* Electric Cable : 12.7/22(24)kV single core XLPE insulated cables – armoured

7 MS 2115* Electric Cable : 6.35/11(12)kV three core XLPE insulated cables – non-armoured

8 MS 2116* Electric Cable : 6.35/11(12)kV three core XLPE insulated cables –armoured



11 MS 2119* Electric Cable : 19/33(36)kV three core XLPE insulated cables –armoured

12 MS 2120* Electric Cable : 19/33(36)kV three core XLPE insulated cables –armoured

13 MS 2104:2007 Electric Cable and Wire: 600/1000(Um = 1200) V single core XLPE insulated cable – non-armoured

14 MS 2105:2007 Electric Cable and Wire: 600/1000(Um = 1200) V single core XLPE insulated cable –armoured

15 MS 2106:2007 Electric Cable and Wire: 600/1000(Um = 1200) V multi core XLPE insulated cable –non-armoured

16 MS 2107: 2007 Electric Cable and Wire: 600/1000(Um = 1200) V multi core XLPE insulated cable –armoured

17 MS 2100:2006 Electric Cable and Wire: 600/1000(Um = 1200) V single core PVC insulated cable – non-armoured

18 MS 2101:2006 Electric Cable and Wire: 600/1000(Um = 1200) V single core PVC insulated cable –armoured

19 MS 2102:2007 Electric Cable and Wire: 600/1000(Um = 1200) V multi core PVC insulated cable –non-armoured

20 MS 2103: 2007 Electric Cable and Wire: 600/1000(Um = 1200) V multi core PVC insulated cable –armoured

21 MS 2112-1: 2009 Electric Cable and Wire: Polyv iny l Chloride(PVC) insulated cables of rated voltages up to and including 450/750 V – Part 1 : General requirements

22 MS 2112-2: 2009 Electric Cable and Wire: Polyv iny l Chloride(PVC) insulated cables of rated voltages up to and including 450/750 V – Part 2 : Test Methods

23 MS 2112-3: 2009 ** Electric Cable and Wire: Polyv iny l Chloride(PVC) insulated cables of rated voltages up to and including 450/750 V – Part 3 : Non-sheathed cables for fixed wiring

24 MS 2112-4: 2009 ** Electric Cable and Wire: Polyv iny l Chloride(PVC) insulated cables of rated voltages up to and including 450/750 V – Part 4 : Sheathed cables for fixed wiring

25 MS 2112-5: 2009 ** Electric Cable and Wire: Polyv iny l Chloride(PVC) insulated cables of rated voltages up to and including 450/750 V – Part 5 : Flex ible cables

26 MS 2112-6: 2009 ** Electric Cable and Wire: Polyv iny l Chloride(PVC) insulated cables of rated voltages up to and including 450/750 V – Part 6 : Cables for Lifts and flex ible connections

27 MS 2121* Telecommunication Cable : Plastic Twin pair,triple and unit types, internal cable

28 MS 2122* Telecommunication Cable : Jumper cable

29 MS 2123* Telecommunication Cable : Self supporting drop wire

30 MS 2124* Telecommunication Cable :Fully Filled Unit Twin moisture barrier polyethy lene sheathed cable (FF PEUT)

31 MS 2125* Telecommunication Cable :Integral Barrier Unit Twin moisture barrier polyethy lene sheathed cable (IB PEUT)

32 MS 2126* Telecommunication Cable :Polyethy lene Insulated 25 Pair Unit Twin moisture barrier polyethy lene sheathed cable (FS PEUT)

MV-XLPE

Telecoms

LV-PVC

LV-XLPE

450/750V-PVC

Overview of Standards & Quality of Cables

3.7kV - 36kV MV BS/IEC/Utility IEC/MS Low Adequate control on test & inspection

1.2kV - 3.6kV LV BS/IEC/Owner IEC/MS Low Adequate control on test & inspection

Existing/Prev New

Above 170kV EHV Utility Utility Nil High scrutiny at all levels

37kV - 170kV HV IEC/Utility IEC/Utility VLow High sampling rate of test & inspection

Um (max voltage) Class Risk Control on Quality & InspectionRef Stds & Specifications

Below 1.2kV ELV BS/MS MS High Minimum or no control

SUB-STANDARD CABLES

Cables which are not designed,

constructed, test approved, installed or

used in accordance to their prescribed

standards and/or specifications

The development of national standards for electric cables takes into account

the principles and norms as established internationally, current prevailing

conditions and local practices. It is important to understand that these

aspects are majorly unbeknown to buyers and users, hence failure to comply

on critical aspects may present an undetermined risk on safety.

Myths of Sub-Standard Cables

• Conductors are smaller due to “technological improvements”

• Copper purity is higher

• Able to withstand higher temperatures hence more current

• The standards have “changed”

• “There is no problem, it still works..”

Anatomy of Sub-Standard Cables

Sub-Standard Cables - Electrical PropertiesItem

Reference STD 07ED100 07ED099 07ED098

Conductor

- resistance ohm/km 26 29.8 69.3 112

- equiv area sqmm 0.731 0.638 0.274 0.170

Flexible Cable 40/0.16mm (0.75sqmm) x 3C

Current rating amp 7.5 6.5 2.8 1.7

Short cct rating amp 84.0 73.3 31.5 19.5

Voltage drop mv/A/m 63 72 168 271

Max length (2.5% drop) metres 14 12 5 3

Detecting Sub-Standard Cables (DIY)

• Check labels and markings for size, type,

manufacturer name/logo and product standard

• Verify physical measurements against

manufacturers’ data

• Estimate the cross-sectional area of conductor by

physical measurement i.e. area x number of wires

• Conduct a conductor d.c. resistance measurement

to the Standards

NON-STANDARD CABLESCables which are designed and constructed to

other standards which may not comply to the

prevailing requirements & regulations on test

approvals and/or installation conditions

The development of national standards for electric cables takes into account

the principles and norms as established internationally, current prevailing

conditions and local practices. It is important to understand that these

aspects are majorly unbeknown to buyers and users, hence failure to comply

on critical aspects may present an undetermined risk on safety.

Basic Design Elements

• CONDUCTOR

- determines base current ratings

• INSULATION

- determines voltage / stress levels

• PROTECTION

- determines installation conditions

Empirically..

Cable type Voltage PrimaryService life

Low Med

Bare Conductors

All Reinforced 35 40

All Non-reinforced 25 35

Paper insulated, metal sheath

All Fluid filled 35 50

All Solid 30 40

Thermosets (XLPE, EPR)

All Metal sheathed 30 40

All Foil laminated 25 35

All Water tight 25 35

All Armoured/Ducted 25 35

All Non-armoured 15 25

Thermoplastics(PVC, PE, EVA)

>3.3kV All types 10 20

0.6/1kV Armoured/Ducted 25 35

0.6/1kV Non-armoured 15 25

<1kV Armoured/Ducted 15 25

<1kV Non-armoured 10 20

<1kV "Sub-standard" <5 --

THREE CORE XLPE CABLE(Lead Sheathed)

Conductor

Conductor

Screen

XLPE

Insulation

Insulation

Screen

Copper Tape

Screen

Binder Tape

Fillers

Separation

Sheath

Lead Sheath

Bedding

sheath

Armour Wires

Oversheath

Preferred for waterlogged

environments

Conductor Metals

VR @ 20oC Density Mass 1990 2015

(W.mm2/km) (gm/cm3) (kg/km) (US$/km) (US$/km)

Silver 16.4 10.5 172.2 29,205 116,044

Copper 17.2 8.89 152.9 255 799

Gold 24.4 19.3 470.9 3,925,590 19,789,913

Aluminium 28.3 2.7 76.4 110 112

Tin 124 7.29 904 4,742 14,122

Lead 214 11.4 2440 754 4,243

Metals

• Copper– Highly Conductive– Good Mechanical

Properties– Relatively Easy to

Process– Usually Annealed

• Aluminium– 60% conductance of

copper at same size– Half the weight of

copper at the same conductance

Insulation Types

• Common types

– 70oC PVC (Polyvinyl Chloride)

– 70oC PE (Polyethylene)

– 90oC XLPE (Cross linked PE)

– 90oC Rubber (EPR,EVA)

– 65oC PILC (Paper insulated)

Mechanical Protection

• Cables need to be mechanically protected against external damage & installed environments

• PRIMARY – by the insulation

• SECONDARY• double insulation and/or sheaths• armour or reinforcement when exposed to potential

damage (direct in ground)• barriers to prevent ingression of moisture, oils,

solvents etc.

Electrical Protection

• Cables need to be electrically protected against damage to adjacent cables, connecting equipment and for safety of users against electrical hazards

• PRIMARY – by the insulation & sheaths

• SECONDARY

- by conductive layer(s) for the safe transfer of leakage currents, to be appropriately sized to meet system ratings and/or suitable grounding or bonding methods against leakages, transients and lightning

Protection from Pest Attack

Method Features

Mixing termite repellent in surrounding earth

Environmental problem

Coating oversheath with termite repellent

Difficult to apply Health problem

Aldrin & Dieldrin Effective but use is however banned in many countries

Mixing termite repellent into cable sheaths Copper naphthanate,

Cypermethrin Alternative to Aldrin & Dieldrin, reasonably effective

Polyethylene Sheath Slows down attack

Common metal sheaths Slows down attack

Tape armour Good protection from large insects and rodents

Nylon Sheath Resistant to termites, but difficult to manufacture

Property PVC Polyethylene LSOH

Tensile (N/sqmm) 15 25 10

Elongation 150% 300% 100%

Density 1.3 - 1.5 0.91 - 0.96 1.4 - 1.6

Physical Soft and flexible Hard and rigid Semi-hard and rigid

Abrasion Resistance Poor Excellent Acceptable

Hot indentation Acceptable Excellent Good

Impact Resistance (thick slab) Good Poor Poor

Stress cracking Resistant Variable (dependent on

molecular weight i.e.

density)

Variable (dependent on base

compound and mix)

Moisture Absorbs moisture with

prolonged contact

Negligible absorption Absorbs and retains moisture

within a short time

Vapour permeability Reasonably permeable Resistant Permeable

High temp. performance Increased ageing at higher

temps.

Improved thermal & ageing

performance

Generally stable

Low temp. performance Brittle at sub zero Stable at sub zero Generally stable

Resistance to chemicals Good Excellent Poor

Fire Performance Flame retardant, emits toxic

fumes & smoke

Low OI, burns without

toxic fumes

Flame retardant, low smoke &

no toxic fumes

Processability Readily extrudable Extrudable Extrudable with special tools

Compound Compounded with

additives and fillers

Homogeneous Highly filled base compound

with additives and fillers

InstallationConditions :

Direct in Ground - Dry Excellent Excellent Good

Direct in Ground - Wet Good (short term only) Excellent Not Recommended

Exposure to UV light Resistant Good (require UV resistant

additives)

Variable (dependent on base

compound and mix)

EXTERNAL

End of Part 1

UV Degradation by Colours

• Exposure to ultraviolet (UV) radiation may cause the significant degradation of many materials. UV radiation causes photooxidative degradation which results in breaking of

the polymer chains, produces free radical and reduces the molecular weight, causing deterioration of mechanical properties and leading to useless materials, after an unpredictable time.

• The Star-Spangled Banner is a case in point. Both the dyes and the wool of our country's most famous flag have been seriously light-degraded over time. And as expected, the

red dye is more faded than the blue. "The red dyes are more susceptible to fading because they look red and thus absorb blue, and blue is the higher-energy light," notes David Erhardt of the Smithsonian Center for Materials Research and Education, who assisted the flag's conservation project.

Water Treeing

• Formation of “tree-like” structures in polyolefins such as PE and XLPE.

• Reduces the breakdown strength of insulation resulting in “electrical trees”

• Degrades with time, electrical stress, frequency and water pressure

• “Bow ties” within insulation due to voids and contaminants

• “Vented trees” from screen interface protrusions and imperfections

Moisture Barrier for HV XLPE Cables

• Extruded Lead Sheath (preferred)

• Extruded Aluminium Sheath

• Metallic Foil Laminate (most economical but least effective)

A radial moisture barrier is required to prevent the

initial ingress of moisture into the cable

In the event of damage to the radial moisture barrier

longitudinal water blocking is essential• Using tapes and yarns loaded with swellable material

or “solid” compounds

• Strategically positioned underneath and between extruded layers, within metal screens, armour or conductor

IEC 60287 Part 1-1: Current rating equations (100 % load factor) and calculation of losses - General

Circuit Analogy – Heat Transfer

Temperature Difference

Conductor

Insulation

Metal Sheath

Armour

Bedding ProtectiveFinish

Soil

CableSurface

GroundSurface

Current Rating Calculations

Cable Current Rating Considerations

• Cable laying conditions

• Ambient & operating temperatures

• Lay configuration

• Bonding system

• External heat sources (including nearby cables)

Thermal Conditions

• Laid direct in ground

• Ground temperature 25oC

• Depth of laying 1000 mm

• Soil TR 1.2 Km/W

System Configuration

• Single circuit

• In trefoil formation

• Specially bonded without transposition

Case Study:630sqmm Alum XLPE 132kV Cable

Trefoil Trefoil

Special Special

Air Air

96 96

25 25

--- ---

--- ---

90 90

0.0223 0.0223

0.0088 0.0088

62 62

0.0014 0.0013

0.5323 0.5323

0.0574 0.0574

− −

− −

− −

0.5097 0.4774

55.2 64.2

59.1 43.8

0.31 0.31

0.08 0.06

976 840223.18 192.08

Trefoil Trefoil

Special Special

Ducts Ducts

160 96

25 25

1000 1000

1.2 1.2

90 90

0.0223 0.0223

0.0031 0.0088

61.7 62

0.0027 0.0013

0.5323 0.5323

0.0918 0.0918

0.2807 0.1415

0.036 0.0189

1.4833 1.7779

1.8000 1.9382

73.3 74.2

26.8 25.3

0.31 0.31

0.07 0.03

659 639150.61 146.16

Lay configuration −− Trefoil

Sheath bonding −− Special

Cable laying condition −− Ground

Phase axial spacing mm 96

Ambient lay temperature °C 25

Depth of Laying mm 1000

Soil thermal resistivity K.m/W 1.2

Max. conductor temperature °C 90

Skin effect −− 0.0223

Proximity effect −− 0.0088

AC resistance at max. temp. μohm/m 62

Metallic covering loss factor −− 0.0013

Therm. resistance − Insulation K.m/W 0.5323

Therm. resistance − Oversheath K.m/W 0.0918

Therm. resist. cable to ducts K.m/W −

Therm. resist. of ducts K.m/W −

Therm. resist. outside ducts K.m/W −

Therm. resistance − External K.m/W 1.7779

External surface temperature °C 73.1

Conductor loss per phase W/m 27

Dielectric loss per phase W/m 0.31

Metallic cov. loss per phase W/m 0.04

Calculated ratings Amps 660Equivalent capacity mva 150.97

Manner of Cable Laying

STD







Soil thermal resistivity K.m/W 1.2Max. conductor temperature °C 90
















oC amos "factor"

15 709 1.074

20 685 1.038

25 660 1.000

30 634 0.961

35 607 0.920

Trefoil

Special

Ground

96

35

1000

1.290

0.0223

0.0088

62

0.0013

0.5323

0.0918

−

−

−

1.7779

75.7

22.9

0.31

0.03

607138.87

Δθ is the conductor temperature rise above the ambient temperature (K);

NOTE The ambient temperature is the temperature of the surrounding medium under normal conditions, at a situation in which cables are installed, or are to be installed, including the effect of any local source of heat, but not the increase of temperature in the immediate

neighbourhood of the cables due to heat arising therefrom.

InsulationMaximum Conductor

Temperature (oC)

PVC 70

Polyethylene 70

Butyl Rubber 85

EPR 90

XLPE 90

Natural Rubber 60

Impregnated Paper 65 - 80

Temperature “Rise”

Thermal Resistances : T1,T2,T3,T4

Cable Laying

• In Air – on racks, bridges, along walls, suspended on poles (aerial)

• Laid in open/closed troughs, tunnels, in conduits (exposed)

• Laid Direct in ground as-is or in pipes/ducts

• Underwater, submarine or river crossing

Bending Radii

No of

Cores

With

Former

Without

Former

Laid

Direct

Laid in

Ducts

33kV

Armoured1 15D 20D

3 12D 15D

33kV

Unarmoured1 12D 15D

3 10D 12D

66 - 132kV 1 15D 20D 30D 35D

D = Cable Diameter

STD























Trefoil

Special

Ground

96

25

500

1.290

0.0223

0.0088

62

0.0013

0.5323

0.0918

−

−

−

1.3807

69.8

32.4

0.31

0.04

723165.25

mm depth amps "factor"

500 723 1.095

750 684 1.036

1000 660 1.000

1250 643 0.974

1500 631 0.956

T4 : Depth of Laying

STD























soil Km/w amps "factor"

0.9 731 1.108

1.0 705 1.068

1.1 682 1.033

1.2 660 1.000

1.5 607 0.920

2.0 540 0.818

Trefoil

Special

Ground

96

25

1000

0.9

90

0.02230.0088

62

0.0013

0.5323

0.0918

−

−

−

1.3334

69.3

33.2

0.31

0.04

731

167.23

T4 : Soil thermal resistivity

oC amos "factor"

15 709 1.074

20 685 1.038

25 660 1.000

30 634 0.961

35 607 0.920

mm depth amps "factor"

500 723 1.095750 684 1.036

1000 660 1.000

1250 643 0.974

1500 631 0.956

soil Km/w amps "factor"

0.9 731 1.1081.0 705 1.068

1.1 682 1.033

1.2 660 1.000

1.5 607 0.920

2.0 540 0.818

Trefoil

Special

Ground

96

35

500

0.9

90

0.0223

0.0088

62

0.0013

0.5323

0.0918

−

−

−

1.0355

69.3

33.1

0.31

0.04

731167.07

STD

Lay configuration −− Trefoil Trefoil Trefoil Trefoil

Sheath bonding −− Special Special Special Special

Cable laying condition −− Ground Ground Ground Ground

Phase axial spacing mm 96 96 96 96

Ambient lay temperature °C 25 35 25 25

Depth of Laying mm 1000 1000 500 1000

Soil thermal resistivity K.m/W 1.2 1.2 1.2 0.9

Max. conductor temperature °C 90 90 90 90

Skin effect −− 0.0223 0.0223 0.0223 0.0223Proximity effect −− 0.0088 0.0088 0.0088 0.0088

AC resistance at max. temp. μohm/m 62 62 62 62

Metallic covering loss factor −− 0.0013 0.0013 0.0013 0.0013

Therm. resistance − Insulation K.m/W 0.5323 0.5323 0.5323 0.5323

Therm. resistance − Oversheath K.m/W 0.0918 0.0918 0.0918 0.0918

Therm. resist. cable to ducts K.m/W − − − −

Therm. resist. of ducts K.m/W − − − −

Therm. resist. outside ducts K.m/W − − − −

Therm. resistance − External K.m/W 1.7779 1.7779 1.3807 1.3334

External surface temperature °C 73.1 75.7 69.8 69.3

Conductor loss per phase W/m 27 22.9 32.4 33.2

Dielectric loss per phase W/m 0.31 0.31 0.31 0.31

Metallic cov. loss per phase W/m 0.04 0.03 0.04 0.04

Calculated ratings Amps 660 607 723 731

Equivalent capacity mva 150.97 138.87 165.25 167.23

660A x 0.920 x 1.095 x 1.108 = 737A

Combined effects of temperature rise, depth of laying and soil Tr

Consideration of external heat sources

A B C D

132kV 1200 Cu 11kV 3c240 Al 132kV 1200 Cu 33kV 630 Al

Uo 76000 6350 76000 19000

TanD 0.001 0.004 0.001 0.004

MVA 150.1 5.0 150.1 30.1

Amps 656.5 263.1 656.5 525.8

Cond temp oC 48.6 69.2 48.6 67.9

Cond AC ohm/km 0.0178 0.1514 0.0178 0.0576

Capacitance mF/km 0.2389 0.4552 0.2389 0.3041

Sheath Loss factor 0.0082 0.0068 0.0082 0.0032

Conductor W/m/ph 7.6739 10.4794 7.6739 15.9254

Dielectric W/m/ph 0.4335 0.0231 0.4335 0.1380

Sheath W/m/ph 0.0628 0.0716 0.0628 0.0516

TOTAL W/m/ckt 24.510 31.722 24.510 48.345

Soil resistivity Km/W 1.2 1.2 1.2 1.2

Depth to center mm 1500 1100 1500 1000

vert horiz 0 250 500 1800

A 1500 0 1.0000 5.5374 6.0828 1.6490

B 1100 250 5.5374 1.0000 5.5374 1.6804

C 1500 500 6.0828 5.5374 1.0000 2.0231

D 1000 1800 1.6490 1.6804 2.0231 1.0000

A Delta temp 0.0000 8.0119 8.4516 2.3414

B Delta temp 10.3694 0.0000 10.3694 3.1447

C Delta temp 8.4516 8.0119 0.0000 3.2984

D Delta temp 4.6182 4.7925 6.5058 0.0000

TOTAL 23.44 20.82 25.33 8.78

FINAL Cond temp oC 72.0 90.0 73.9 76.7

Case C

Inductive losses

For single-core cables with sheaths bonded at both ends of an electrical section, only the lossdue to circulating currents in the sheaths need be considered (see 2.3.1, 2.3.2 and 2.3.3). Anelectrical section is defined as a portion of the route between points at which the sheaths orscreens of all cables are solidly bonded.

For a cross-bonded installation, it is considered unrealistic to assume that minor sections areelectrically identical and that the loss due to circulating currents in the sheaths is negligible.Recommendations are made in 2.3.6 for augmenting the losses in the sheaths to take accountof this electrical unbalance.

2.3 Loss factor for sheath and screen (applicable to power frequency a.c. cables only)

The power loss in the sheath or screen (λ1) consists of losses caused by circulating currents

( λ1′ ) and eddy currents ( λ1′′ ), thus: λ1 = λ1′ + λ1′′

T1 : Inductive losses

Earthing and Bonding

• Solid Bonding

• Special Bonding

– Single End Point

– Mid Point

– Cross Bonding

Solid Bonding

Link Box

Outdoor Sealing Ends

Normal Bonding Strand

Link Box

Single End Point Bonding

Link BoxWith SVL

Link BoxEarth ContinuityConductor


Inner ConductorOuter Conductor

Concentric Bonding Strand

Cross Bonding System

Link Box


Link Box

Cross Bonding Link BoxWith SVL's

Insulated Straight Through Joints

Earth ContinuityConductor

Inner ConductorOuter Conductor

Concentric Bonding Strand




Touching or Spaced Touching




Soil thermal resistivity K.m/W 1.2

Max. conductor temperature °C 90




Metallic covering loss factor −− 0.0013Therm. resistance − Insulation K.m/W 0.5323











Trefoil

Solid

Ground

Touching

96

25

1000

1.2

90

0.0223

0.0088

62

0.4050.5323

0.0918

−

−

−

1.7779

76.4

20.6

0.31

8.33

576131.7

Flat

Special

Ground

Touching

96

25

1000

1.2

90

0.0223

0.0088

62

0.00080.5323

0.0574

−

−

−

1.7126

73.4

28.2

0.31

0.02

675154.23

Flat

Solid

Ground

Touching

96

25

1000

1.2

90

0.0223

0.0088

62

0.23580.5323

0.0574

−

−

−

1.7126

75.6

23.9

0.31

5.64

621141.95

Lay configuration : Trefoil & Flat at Solid & Special bondings

Lay configuration −−

Sheath bonding −−

Cable laying condition −−

Touching or Spaced

Phase axial spacing mm

Ambient lay temperature °C

Depth of Laying mm

Soil thermal resistivity K.m/W

Max. conductor temperature °C

Skin effect −−

Proximity effect −−

AC resistance at max. temp. μohm/m

Metallic covering loss factor −−

Therm. resistance − Insulation K.m/W

Therm. resistance − Oversheath K.m/W

Therm. resist. cable to ducts K.m/W

Therm. resist. of ducts K.m/W

Therm. resist. outside ducts K.m/W

Therm. resistance − External K.m/W

External surface temperature °C

Conductor loss per phase W/m

Dielectric loss per phase W/m

Metallic cov. loss per phase W/m

Calculated ratings Amps

Equivalent capacity mva

Flat Flat Flat

Special Special Special

Ground Ground Ground

Touching Spaced Spaced

96 191 287

25 25 25

1000 1000 1000

1.2 1.2 1.2

90 90 90

0.0223 0.0223 0.0223

0.0088 0.0022 0.001

62 61.6 61.5

0.0008 0.0025 0.00350.5323 0.5323 0.5323

0.0574 0.0574 0.0574

− − −

− − −

− − −

1.7126 1.6109 1.4582

73.4 72.6 71.3

28.2 29.5 31.7

0.31 0.31 0.31

0.02 0.07 0.11

675 692 717154.23 158.16 163.99

Flat Flat Flat

Solid Solid Solid

Ground Ground Ground

Touching Spaced Spaced

96 191 287

25 25 25

1000 1000 1000

1.2 1.2 1.2

90 90 90

0.0223 0.0223 0.0223

0.0088 0.0022 0.001

62 61.6 61.5

0.2358 0.7849 1.09510.5323 0.5323 0.5323

0.0574 0.0574 0.0574

− − −

− − −

− − −

1.7126 1.6109 1.4582

75.6 78.2 78.6

23.9 18.5 17.5

0.31 0.31 0.31

5.64 14.53 19.2

621 548 534141.95 125.35 122.04

1 2

Lay configuration : Flat, Solid & Specially bonded, Touching & Spaced

√Single layer

Flat formation

√

√

Two Tiers in

Flat formation

Single layer

in Trefoil

Electric Cables to be laid

on the periphery of duct

banks ( not recommended

for long spans )

For a safe and long service life, electric

cables are herein prescribed to be..

• Designed to the correct standards, with

consideration of its expected rating and

environment in service

• Installed in the correct manner as per

recommended guidelines

• Maintained (where applicable) and

operated within its limits and condition of

service

• “Prophesized” for end of life

Thank you !

Safety & Survival of Electric Cables

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